Transmission circuit



D. G. GRlMLEY TRANSMISSION CIRCUIT Oct. 11, 1932.

Filed Aug. 51, 1926 w, W6 w by Any narran ,Stef-S increasing theamplification of low frequen- Patented oei. ii, i932 Aer rice

DGNALD Gr. GRIMLEY, OF REDGEWOOD, IEW' JERSEY, ASSIGNOR TO BELLTELEPHONE LABORATGRES, NCOEFGEJATED, 0F NEW' YORK, N. Y., A CORPORATIONOF NEW YORK rnnnsirissioii cincurr Application filed August S1, 1926.Serial N0.`132,671.

rlhis invention relates toelectrical transmission circuits andparticularly to amplifier circuits.

An object of this invention is to control the transmissioncharacteristic of electrical circuits.

A specific object of the invention is to ob-V tain uniform amplificationover a wide range of frequencies.

' In the copending application of Horace lVhittle, Serial No. 132,601,filed August 30, 1926, now Patent No. 1,739,699, issued December 17,1929, there is disclosed andl claimed an arrangement which may beemployed for cy waves to obtain uniform amplification over a Wide rangeof frequency, this arrangement comprising aV multi-branch core structurehaving input and output transformer windings mounted thereon in such away as to obtain coupling therebetween, the coupling being cies than forothers.

rlhe present invention is a species of the y generic invention of thatapplication in which the input and output transformers, which arepreferably of the shell type, have one leg of their cores in common. Byregulating the reluctance of the common leg it is possible to controlthe coupling between the transformers and consequently the transmissioncharac# teristic of the circuit.

In one embodiment of this invention thek core of an interstagetransformer of a multistage amplifier has one legv in common with thecore of the input transformer of the preceding stage and another leg incommon with Fig. 1 of which shows an embodiment of this f invention in asingle stage amplifier and Fig.

2 of which shows an embodiment of this invention in a multi-stageamplifier.

Referring to the single stage amplifierl cirgreatei for currentsofcertain frequen-- cuit of Fig. 1 there'are shown two E shaped coresections 41 and 5 which are combined with a single I shaped section 6 toform two shell type transformer cores having a common leg formed'by theI section 6. 'Mounted on a central branch of the E section l are twowindings 7 and 8 which function as an input transformer for theamplifier tube 9, the primary y winding 7 being connected to the inputterminals of the amplifier circuit, the secondary winding 8 Vbeingconnected to the input electrodes of the tube 9 through the grid4biasing' ,battery 10. Mounted on the central leg of the .E section 5.are two windings 11 and 12 which serve as output windings for theamplifier tube 9, the primary winding 11 being connected to the outputelectrodes of the'tube 9 through a plate battery 13, and the second-lary winding 1-2 being connected to the output terminals of the amplifiercircuit.

If'the leg 6 is of such cross section that its reluctance is low.compared to the reluctance of the remainder of the magnetic circuit,there will be practically no coupling between the input and outputtransformer windings. However, if gthe reluctance of the leg 6 isincreased, for example, by reducing its cross section or by theintroduction of an air gap, coupling may be produced between thewindings which will cause a feed-back from the output transformer to theinput transformer causing an increased amplification particularlv at thelow frequencies.

Fig. 2 shows a similararrangement for a multi-stage amplifier. In thiscase there arek shown three Eshaped laminations 111, A15 and 16 and oneI shaped lamination 17 which are combined to form three shell typetransformer cores, the central one of which has a leg in common witheach of .the outer onesi Mounted on a central branch of the core section14e are transformer windings 18 and 19 which serve as an inputtransformer for the first stage vacuum tube 20, the primary winding 18being connect-ed to the input terminals secondary winding19 beingconnected to the input Velectrodes of the tube. Mounted on the centralbranch of the core section 15 are two windings 21 and 22 which serve asan inter-.

of the multi-'stage amplifier circuit and the

